This invention relates in general to the field of mass storage devices and more particularly to a pre-amplifier and a device for determining faults in a head.
A hard disk drive includes a stack of magnetically coded platters that are used for storing information. The magnetically coded platters are mounted together in a stacked position through a spindle which may be referred to as a platter stack. The platter stack is typically rotated by a motor that is referred to generally as a spindle motor or a servo motor. A space is provided between each platter to allow a read/write head or slider to be positioned on each side of the platter so that information may be stored and retrieved. Information is stored on each side of each platter and is generally organized into sector track zones and cylinders. Each of the read/write heads or sliders is mounted into one end of the dedicated suspension arm so that each of the read/write heads may be positioned as desired. The opposite end of each of the suspensions arms is coupled together at the voice coil motor to form one unit or assembly that is positionable by a voice coil motor. Each of the suspensions arms is provided in a fixed position relative to each other. The voice coil motor positions all of the suspensions arms so that the read/write head is properly positioned for reading or writing information. The read/write heads or sliders may move from at least one inner diameter to an outer diameter where data is stored. This distance may be referred to as a data stroke.
Hard disk drives also include a variety of electronic circuitry for processing data input for controlling its overall operation. The electronic circuitry may include a pre-amplifier, a read channel, a write channel, a servo controller, a motor control circuit, a read only memory open (ROM), a random access memory (RAM) and variety of disk control circuitry to control the operation of the hard disk drive and to properly interface the hard disk drive to the system bus. The pre-amplifier may contain a read pre-amplifier and a write pre-amplifier that is also referred to as a write driver. The pre-amplifier may be implemented in a single integrated circuit or may be a separate integrated circuit such as read pre-amplifier, a write pre-amplifier, or a write driver. The disk control circuitry generally includes a separate microprocessor for executing instructions stored in memory to control the operation and interface of the hard disk drive. The hard disk drive performs read, write and servo operations when storing and retrieving data. The write operation includes retrieving data from a system bus and storing to data in the RAM. The microprocessor schedules a series of events to allow the information to be transferred from the ROM to platters through the write channel. Before the information is transferred, the read and write heads are positioned on the appropriate track, and the appropriate sector of the track is located. The data from the RAM is then communicated to the write channel as a digital write signal. The write channel processes the digital write signal and generates an analog write signal. In doing this, the write channel may encode the data so that the data can be more reliably retrieved later. The digital write signal may then be provided to an appropriate read/write head after first being amplified by the pre-amplifier. In read operation, the appropriate sector is read, is located and data that has previously written to the platter is read. The appropriate read/write head senses the changes in the magnetic flux and generates a corresponding analog read signal. The analog read signal is provided back to the electronic circuitry where the pre-amplifier amplifies the analog read signal. The amplified analog read signal is then provided to the read channel where the read channel conditions the signals and detects xe2x80x9czerosxe2x80x9d and xe2x80x9conesxe2x80x9d from the signal to generate a digital read signal. The read channel may condition the signal by amplifying the signal to an appropriate level using automatic gain control (AGC) technique. The read channel may then filter the signal to eliminate unwanted high noise, equalize the channel, detect xe2x80x9czerosxe2x80x9d and xe2x80x9conesxe2x80x9d from the signal and format the digital read signal. The digital read signal is then transferred from the read channel and stored in the RAM. The microprocessor may then communicate to the host that data is ready to be transferred. The read channel may be implemented using any of a variety of known or available channels. For example, the read channel may be implemented as a peak detection type read channel or as a more advanced type of read channel utilizing discreet time signal processing. The peak detection read channel involves level detecting the amplified analog read signal and determines if the wave form level is above a threshold level during a sampling window. The discreet time signal processing type read channel synchronously samples the amplified read signal using a data recovery clock. The sample is then processed through a series of mathematical manipulations using signal processing theory to generate the digital read signal. There are several types of discreet time signal processing read channels such as partial response, maximum likelihood (PRML) channel and extended PRML channel or enhanced extended PRML channel, a fixed delay tree search channel and a decision feedback equalization channel.
As the disk platters are moving, the read write heads must align or stay on a particular track. This is accomplished by the servo operations through use of the servo controller provided in a servo control loop. In servo operation, a servo wedge is read from the track that generally includes track identification information and track misregistration information. The track misregistration information may also be referred to as position error information. The position error information may be provided as servo bursts that may be used during read and write operations to ensure that the read write heads are properly aligned on the track. As a result of receiving the position error information, the servo controller generates a corresponding control signal to position the read write heads by positioning the voice coil motor. The track identification information is also used during read and write operations so that a track may be properly identified.
Hard disk drive designers strive to provide higher capacity drives that operate at a high signal to noise ratio and a lower bit error rate. To achieve higher capacities, the aerial density of the data stored on each side of the platter must be increased.
It can be appreciated that there is a need for detecting an open circuit or any kind of fault in the write head. Such a fault would prevent data from being written to the medium and without such a fault indication, the fault would go unnoticed or undetected. Consequently, it is desirable to detect this fault operation. Importantly, it necessary to detect WDI to low open head, a short cross, which is a cross of the X and Y, and short to ground which is when the head is short to ground. The fault, if undetected, could result in loss of data.
The present invention detects fault conditions during operation of the head for example, during read write operations by a write unsafe detector (WUS). The present invention uses advantageously the inductive property of the head which cause a xe2x80x9ckickbackxe2x80x9d when the current is switched through the head. This kickback causes the voltage on one side of the magnetic head to rise above the normal operating value. The present invention recognizes that this kickback pulse would not be present if the head were open. By detecting the presence of this pulse during each half of the write cycle, a write unsafe circuit can determine if the head is in a normal operation or has opened.